how do these two heavy bags look?

http://store.everlastboxing.com/rocky-70-lb-heavy-bag.html

http://www.sugarrays.co.uk/shop/product.php?productid=4725&cat=123&page=1

http://www.ringside.com/DETAIL.ASPX?ID=25250

http://www.ringside.com/DETAIL.ASPX?ID=25262

Are the canvas bags ok? Is the weight suitable to increase my power?

any help


thanks